Field of the Invention
The present invention relates to an organic light emitting device which may improve efficiency and an organic light emitting display having the same.
Discussion of the Related Art
As the information age has arrived, the field of displays visually expressing electrical information signals has rapidly developed. Thus, various flat display devices to enhance performance, such as reduced thickness, light weight and low power consumption, have been researched.
As representative examples of flat display devices, there are liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), electro luminescent displays (ELDs), electro-wetting displays (EWDs), and organic light emitting displays (OLEDs), etc.
Thereamong, the OLED is a display device that displays an image using organic light emitting devices which emit light by themselves.
The organic light emitting device includes first and second electrodes opposite to each other and an organic laminate formed between the first and second electrodes. And, the organic light emitting device emits light based on driving current flowing between the first and second electrodes. The organic laminate includes a light emitting layer generating light through recombination of holes and electrons. And, the organic laminate emits light of different colors according to materials of a dopant included in the light emitting layer.
As one method to improve efficiency of the organic light emitting device or to produce white light, a multi-stack structure has been proposed. The multi-stack structure means a structure in which the organic laminate formed between the first and second electrodes includes a plurality of stacks. Here, each stack includes an electron transport layer, a light emitting layer, and a hole transport layer.
FIG. 1 is a cross-sectional view illustrating a general organic light emitting device having a multi-stack structure.
As exemplarily shown in FIG. 1, a general organic light emitting device 10 having a multi-stack structure includes an anode 11 and a cathode 12 opposite to each other, a plurality of stacks 13 and 14 formed between the anode 11 and the cathode 12, a charge generation layer 15 formed between the stacks 13 and 14, a hole injection layer 16 formed between the anode 11 and the plurality of stacks 13 and 14, and an electron injection layer 17 formed between the cathode 12 and the plurality of stacks 13 and 14.
Each of the stacks 13 and 14 includes a hole transport layer (HTL), a light emitting layer (EML), and an electron transport layer (ETL).
The charge generation layer 15 is formed in a multi-layered structure including at least two metals, oxides, and organic matters so as to generate holes and electrons which will be transported to the plurality of stacks 13 and 14.
That is, the charge generation layer 15 serves as a cathode injecting electrons into the stack 13 which is closer to the anode 11 then the other stack 14. Also, the charge generation layer 15 serves as an anode injecting holes into the stack 14 which is closer to the cathode 12 then other stack 13.
The organic light emitting device 10 having a multi-stack structure includes a large number of light emitting layers and may thus has an advantage of increasing efficiency, as compared to an organic light emitting device having a mono structure including one stack. However, the organic light emitting device 10 having a multi-stack structure includes a large number of interlayer boundaries and may thus have disadvantages of high driving voltage and short lifespan.